1. Field of the Invention
The present invention relates to a differential rotation control apparatus and more particularly to a differential rotation control apparatus capable of controlling a wheel rotation speed ratio between left and right wheels with simple control logics over a wide driving range.
2. Discussion of Related Arts
Various ideas of torque distribution control apparatuses between left and right wheels for vehicles have been produced and put into practical use. As a typical type of those apparatuses, there is an apparatus incorporating a coupling (a hydraulic multiple disc clutch is widely used) for variably controlling torque distribution between left and right wheels.
The apparatuses like these are disclosed for example in Japanese Patent Applications 2641724, 2826580 and the like. These apparatuses incorporates gear sets for forcedly differentiating left and right shafts by a hydraulic multiple disc clutch so as to regulate a torque flow from left to right wheels and vise versa besides a mechanical type differential for transmitting power from a power source to left and right wheels.
However, the differential rotation control apparatuses disclosed in the patent applications 2641724, 2826580 have a disadvantage that the upper limit of the controllable rotation speed ratio between left and right wheels is dependent upon gear ratios of the gear sets and therefore the control range of the differential rotation control apparatuses is limited by their mechanical construction. Further, those prior arts need a complicated feedback control with respect to an increase or decrease of torque in order to maintain the rotation speed ratio between left and right wheels at the target rotation speed ratio.